1. Field of the Invention
The present invention relates to a rotary actuator which performs rotary driving of a rotation member using an electromechanical conversion element such as a piezoelectric element.
2. Related Background Art
Conventionally, as a rotary actuator, an electromagnetic motor which uses a combination of a magnet and a coil is popular. Recently, a vibration wave motor which is driven by a traveling vibration wave is known. The vibration wave motor converts a vibration caused upon application of a frequency voltage to an electrostrictive element into rotation or linear motion, as disclosed in Japanese Patent Disclosure (Kokai) No. 29192/1976. Since the vibration wave motor does not require a coil unlike a conventional electromagnetic motor, its structure is simple and compact. During a low-speed rotation state, high torque can be obtained, and its inertial moment is small. Thus, the vibration wave motor has received a great deal of attention.
However, when the conventional vibration wave motor converts the vibration into the rotation or the like, it frictionally drives a moving member such as a rotor which is brought into contact with a vibration member in one direction by a standing vibration wave genreated by the vibration member. Upon forward vibration, the vibration member is in frictional contact with the moving member, and they are separated from each other upon reverse vibration. For this reason, the vibration member and the moving member must have a structure wherein they can be in contact with each other within a very small range, i.e., they can be in point or line contact with each other. Therefore, frictional driving efficiency is considerably degraded. Since the vibration is inertial motion, it is difficult to control it, and to obtain a desired operation.